Hi Gaz,
welcome to the forum   
 
If the car is solid bodywise, then it's worth saving but don't under estimate the amount of work required to recommission it...... I've got exactly the same thing..... a 1984 silver RX7 with the red interior and it's been stored since 1992...... just a an indication, I've had to replace:
Clutch 
Clutch master cylinder
Clutch slave cylinder
All rubber flexible hydraulic lines
Brake master cylinder
Rebuilt all brake calipers
Skimmed brake discs
Full service
New tyres all round
Cooling system overhaul
Refurbished suspension 
New wipers
Refurbished fuel system inc all lines, fuel pump, fuel tank, carb
Etc., Etc., Etc....
My thread detailing what I've done so far is here...
viewtopic.php?f=4&t=268
As Dave says, it's very seldom someone sticks a 7 year old car way and leaves it there if there's nothing wrong with it...... it could be a blown engine which was serious £££££ back in 1992, certainly enough to take it off the road......... these days you can pick up a second hand engine for £100 to get you on the road..... but they were big money back in 1992.
A big plus in the cars favour is that the bodywork won't have been subjected to the last 27 British winters and salt laden roads so it should be, as you say, relatively rust free, which is a very rare thing in one of these cars these days.
What's it worth.... well, I was given mine for free but the money to recommission it will be quite a bit. I personally wouldn't pay more than £300 - £400 for it.... depending upon condition.